Recently, the performance and functionality of digital cameras and digital movie cameras that use some solid-state image sensor such as a CCD and a CMOS (which will be sometimes referred to herein as an “image sensor”) have been enhanced to an astonishing degree. In particular, the size of a pixel structure for use in a solid-state image sensor has been further reduced these days thanks to rapid development of semiconductor device processing technologies, thus getting an even greater number of pixels and drivers integrated together in a solid-state image sensor. And the performance of image sensors has been further enhanced as well. Meanwhile, cameras that use a backside illumination type image sensor, which receives incoming light on its reverse side, not on its front side with a wiring layer for the solid-state image sensor, have been developed just recently and their property has attracted a lot of attention these days. An ordinary image sensor receives incoming light on its front side with the wiring layer, and therefore, no small part of the incoming light would be lost due to the presence of a complicated structure on the front side. In the backside illumination type image sensor, on the other hand, nothing in its photodetector section will cut off the incoming light, and therefore, almost no part of the incoming light will be lost by the device structure.
A camera that uses such a backside illumination image sensor would further expand the range of the image capturing environment. Also, recently, there is a growing demand for performing an image capturing session not just in the daytime but also at nighttime using an infrared ray. To meet such a demand, cameras that are dedicated to performing a shooting session at nighttime using a backside illumination image sensor or cameras that can be used both in the daytime and in the nighttime with the use of such a sensor could be put on the market sometime soon.
While the backside illumination image sensors are being developed, a lot of people have reported results of their researches on the device structures and manufacturing processes of such sensors. Meanwhile, it has also been researched rather extensively how such an image sensor should use the incoming light. For example, Patent Documents Nos. 1 and 2 disclose a technique for arranging an element with reflecting and condensing functions (such as a reflector or a concave mirror) on the principal surface of an image sensor in order to increase the sensitivity. According to such a technique, the light that has come through the back surface of the image sensor and has been transmitted through a photosensitive cell is made to be incident on the same photosensitive cell again , thereby attempting to increase the optical efficiency. On the other hand, Patent Document No. 3 discloses a technique for achieving the same object by getting the transmitted light reflected by a multilayer film. In any case, most of the light that has been transmitted through a photosensitive cell of an image sensor is an infrared ray due to the light absorbing property of silicon. That is why if the light that has once been transmitted through a photosensitive cell is made to be incident on the same photosensitive cell again, then the sensitivity to infrared rays, among other things, would increase.
As for a normal, non-backside-illumination image sensor (which will be referred to herein as a “frontside illumination image sensor), a technique for obtaining a color signal and an infrared signal at the same time is disclosed in Patent Document No. 4, for example. According to Patent Document No. 4, color separation filters for transmitting light rays representing the respective colors of RGB and an infrared pass filter that transmits only an infrared ray (IR) are arranged in a matrix consisting of two columns and two rows as shown in FIG. 13 with respect to photosensitive cells of the image sensor. In this case, the RGB color filters can also transmit the infrared ray. That is why an infrared cut filter is arranged in front of each of those RGB color filters. With such an arrangement, the image capture device disclosed in Patent Document No. 4 produces a color image in the daytime by using the light rays that have been transmitted through the RGB color filters and produces a monochrome image in the nighttime by using an infrared ray that has been transmitted through the infrared filter as a light source. In this manner, by using an infrared cut filter in a part of the image capturing section, a color image and a monochrome image can be produced by using a visible radiation and an infrared ray, respectively.